Frying pan with a welded hollow-core expansion joint

ABSTRACT

A commercial type heating or cooking utensil having a hollowcore expansion joint in the weld seam between the dissimilar metals. The weld seam between the dissimilar metals has a tendency to crack or break due to the continued heating and cooling cycle of the utensil when in operation. A hollow-core expansion joint capable of being welded to each of the metals is laminated between the stainless steel and cast iron of the utensil and when bonded thereto, serves to absorb the stresses induced when the utensil is heated and cooled alternately. Hence, the novel of construction provides an improved stainless steelcast iron cooking utensil capable of withstanding the induced stresses of the heating and cooling cycles accompanying operation, without cracking or breaking at the weld seam.

United States Patent 1 Ryan [ 1 Oct. 23, 1973 FRYING PAN WITH A WELDEDHOLLOW -CORE EXPANSION JOINT [76] Inventor: John Justin Ryan, 14 LeanderCt.,

Toronto, Ontario, Canada 22 Filed: Nov. 22, 1972 21 Appl. No.: 308,702

[52] U.S. Cl 219/438, 13/25, 165/83,

219/421, 219/521, 220/67, 338/316 [51] Int. Cl. F27d 11/02 [58] Field ofSearch 219/389, 421, 432,

[56] References Cited UNITED STATES PATENTS 2,029,038 1/1936 Scott et al174/13 2,233,485 3/1941 Park 219/441 2,512,748 6/1950 Lucke.... 165/832,521,480 9/1950 R0bcrts..... 219/521 X 2,849,148 8/1958 Lohnis 220/672,850,616 9/1958 Hatch 219/433 2,969,448 1/1961 Alexander 13/25 X3,173,121 3/1965 Murry 338/316 X 3,179,731 4/1965 Cash et a1. 219/421 X3,308,225 3/1967 Wells 264/249 3,505,722 4/1970 Ullman 29/401 PrimaryExaminer-Velodymyr Y. Mayewsky Attorney-Casey P. August 57 ABSTRACT Acommercial type heating or cooking utensil having a hollow-coreexpansion joint in the weld seam between the dissimilar metals. The weldseam between the dissimilar metals has a tendency to crack or break dueto the continued heating and cooling cycle of the utensil when inoperation. A hollow-core expansion joint capable of being welded to eachof the metals is laminated between the stainless steel and cast iron ofthe utensil and when bonded thereto, serves to absorb the.

stresses induced when the utensil is heated and cooled alternately.Hence, the novel of construction provides an improved stainlesssteel-cast iron cooking utensil capable of withstanding the inducedstresses of the heating and cooling cycles accompanying operation,without cracking or breaking at the weld seam.

8 Claims, 3 Drawing Figures FRYING PAN WITH A WELDElD HOLLOW-COREEXPANSION JOINT BACKGROUND OF THE INVENTION This invention relates to animproved method for welding stainless steel to cast iron and the weldedarticle obtained therefrom. More particularly, the invention pertains toimprovements in the construction of commercial type heating or cookingutensils which undergo continued heating and cooling cycles when inoperation. The induced stresses arising in the weld seam between thedissimilar metals are of such magnitude as to cause failure of the weldand base metals by cracking or breaking thus rendering the cookingvessel unusable.

DESCRIPTION OF THE PRIOR ART Ferrous alloys comprising substantiallychromium, iron and nickel are referred to in the trade as stainlesssteels. The chromium-nickel stainless steels are those containing nickeland chromium plus other elements to a lesser degree. Thesechromium-nickel stainless steels are known as the austeniticchromium-nickel stainless steels. The nickel being added in sufficientamount to make the steels austenitic and nonmagnetic with improvedductility and conductiveness over the straight chromium steels.

More particularly austenitic stainless steels generally contain fromabout 16-22 percent chromium and at least 8 percent nickel and for thisreason are commonly called 18-8 stainless steels. They are also known asthe 300 series in the SAE rating code (see Table II below).

Cast iron is a high carbon (up to 25 percent) ferritic alloy, porous andvery brittle due to the carbon content but of extreme toughness andresistance to impact stress.

The successful welding of stainless steel to a cast iron base metal haslong been a difficult task due to the tendency of crack and faultformation in the welding-heat affected zone of the dissimilar metals,the low carbide solubility in the stainless steel layer, the porosity ofthe cast iron and the general metallurgical dissimilarities of a highcarbon alloy and a stainless steel. The welds thus formed, in torch orarc-welding, are brittle, greatly lacking in ductility, exhibit a poorresistance to shock or impact, and are unable to endure much bending,shear or other stress.

The prior art has sought to overcome these unsatisfactory conditions ina vast variety of ways, these including inter alia, the altering of thebase composition of the stainless steel alloys, increasing the carbidesolubility in the austenitic or martensitic regions of the iron phasediagram by additive, introducing various hydrocarbon gases or reducinggases, e.g., hydrogen sulfide, during the welding process, etc. Theseseveral variants however, although improving the quality of the weldsdid not afford a weld capable of withstanding the severe stressesbrought about by the continuous heating and cooling cycles experiencedin commercial heating or cooking utensils. Moreover, the occurence ofsuch weld defects as described above is greatly increased during thefabrication of welded cooking utensils having a basin or other curvedshaped, due to the higher stresses conferred on the unit by thegeometrical design, these being additive to the usual coefficient ofexpansion stresses already present in the weld.

Several difficulties exist at present in the art of fabrication ofcommercial cooking or heating utensils, especially those cooking vesselssubject to public display during operation.

In many cases it is highly desirable and indeed mandatory to supply astainless steel cooker for aesthetic, cleaning and other diverspurposes. Thus, breweries, distilleries, bottling plants, commissariesand other commercial outlets concerned with the preparation of cooked orpasteurized foods require vessels and equipment fabricated eitherentirely of stainless steel or, more economically, of a stainless steelexterior welded to a cast iron or steel base which serves as the heatingsurface.

A composite cooking vessel made of cast iron and stainless steel is alsopreferred by a great many professional chefs because 'of the flavourenhancement imparted to the cooked foods owing to the greater porousness of the cast iron cooking surface and its excellent ability foreven heat distribution. These advantages are not as pronounced instainless steel cooking vessels.

Composite welded utensils which continually undergo a two-stage heatingand cooling cycle while in operation, place the weld seam under severestresses due to the vast differences in the coefficients of expansion ofthe two dissimilar metals. For example, in a welded cast iron-stainlesssteel unit these stresses are in the order of 10 p.s.i. and if thisexceeds the material strength of either metal, cracking or breaking willoccur. For instance, the rupture modulus for Meehanite, a registeredtrademark for a typical cast iron found in Table I below, is only 8 X 10p.s.i. In many cases these induced stresses will exceed the materialstrength of both metals. Hence, welded dissimilar metal utensils such ascommercial frying pans, autoclaves, chemical reactors and the like areall subject to weld defects while in continued operation.

In view of the prior art discussion outlined above, it is a prime objectof the invention to provide a method for welding stainless steel to castiron by the laminar insertion of a hollow-core, ferritic metal, tubularexpansion joint between the respective workpieces which, after welding,is capable of absorbing the induced stresses of heating and coolingeffects on the weld seam without any deleterious affects thereto.

A second object of the invention is to provide welded heating or cookingutensils comprised of stainless steelcast iron which will not sufferweld defects such as cracking or breaking while in operation.

Another object of the invention is to provide commercial type cookingutensils having a stinaless steel exterior and a cast iron cookingsurface which are easy to clean, economical to manufacture, acceptableto master chefs and have the desirable weld characteristics describedbeforehand.

It is a further object of the invention to provide a commercial typefrying pan unit having a stainless steel exterior and a welded cast ironcooking surface which will not crack or fault at the weld seam duringcontinued operation.

STATEMENT OF THE INVENTION The present invention seeks to overcome thedifficulties encountered in the prior art by a simple yet novelexpedient. This expedient resides in the laminar insertion of awrought-iron or steel tubular hollow-core expansion joint section havingthe shape of a substantially flattened oval and sandwiching and weldingit between the base metal which is a cast iron and the stainless steelwhich may be either an austenitic or a martensitic stainless steel. Thehollow-core, tubular expansion joint section fulfils two functionssimultaneously firstly, being interstitial in carbon content composition(about 2.5 percent), it bonds well to each of the dissimilar metals;secondly, being hollow-cored, the expansion joint section is able toabsorb the stresses resulting from the heating and cooling cycle of acooking utensil without undue transfer of these stresses to the weldedzone. 7

Although consumable electrodes which are capable of bonding well to boththe stainless steel and cast iron are well known and widely used in theart, the weldment formed therefrom is necessarily solid and inflexible,whereas the combining of a hollow-core member into the weld seam, i.e.,the expansion joint, provides a very slight degree of flexibility afterit is laminated and bonded in thewelded article.

DESCRIPTION OF THE DRAWINGS The invention may be further understood froma description of the accompanying drawings which are designated as FIGS.1-3, wherein;

FIG. 1 is a fragmentary perspective view of the tubular expansion joint,

FIG. 2 is an exploded portion of a cross-sectional elevation of thewelded zone taken along the line 2-2 of FIG. 3,

FIG. 3 is a perspective view of a commercial frying pan utensil.

DESCRIPTION OF A PREFERRED EMBODIMENT A preferred embodiment of theinvention is now described having reference to the foregoing drawings.In FIG. 1 the expansion joint section 1 has been preformed into asubstantially flattened-oval shape from standard wrought iron tubularpipe or fabricated by rolling and shaping from flat wrought ironsheeting. Alternatively, the expansion joint section 1 may be preformedfrom standard steel tubing of appropriate diameter which is inproportion to the dimensions of the welded article. The wall thicknessof joint 1 must also be of sufficient width so as to prevent any burnthrough of the joint member during the welding process. In the fryingpan constructions described herein, this wall thickness is at leastone-sixteenth inch thick. The wrought. iron pipe used for the expansionjoint in a typical frying pan fabrication is rated by the ASME BoilerCode as SA-53. The tubular, hollow-core, flattened-oval shaped expansionjoint member 1 is next welded around the peripheral edge of arectangular shaped, flat cast iron sheet 2, shown in fragmentary view inFIG. 2, and forms the frying pan cooking surface of the frying panutensil 6 depicted in FIG. 3. The weld is effected by conventional arcor torch welding techniques, employing a consumable electrode or rod asthe weldment 5,, and capable of bonding to both the castiron andexpansion joint members. In the frying pan fabrications the rectangularcast iron cooking surface sheets used are normally at least three-fourthinch thick.

An abutment lip 3 illustrated in FIG. 2 has been formed beforehand byreducing and indenting a portion of the wall section 4 of the stainlesssteel jacket housing of the frying pan utensil 6 shown in FIG. 3. Thisabutment lip 3, projects inwardly around the entire wall section 4, andis positioned approximately midway between the top and bottom of thehousing.

The abutment lip 3 serves as a tensioning means to prevent the stainlesssteel jacket housing from distorting during the final welding stage. Thecast iron sheet 2, engirdled with the tubular expansion joint I, is nextaligned and fitted into position with the abutment lip 3 of thestainless steel housing wall 4 and welded in place, using a consumableelectrode which is an SAE 310 or 316 stainless steel rod to form theweldment 5, having reference to FIG. 2. The weld seam can then be handor machine finished to form a smooth integral unit structure comprisedof the stainless steel jacket housing, the welded expansion joint andthe cast iron cooking surface. FIG. 3 illustrates a completed frying panutensil, designated 6 in the drawing, and equipped with an electricheating source (not shown) housed in the trunion gear box 8' of thetilting trunion stand 12. The electric heater is controlled by an ON-OFFregulator switch 7, surmounted on the front panel of the trunion gearbox 8'. The other trunion gear box 8, carries a crankwheel 9 attached toa crankshaft (not shown) which tilts the cooking vessel portion by thegear train in the trunion box, when desired. The frying pan is alsofitted with a hinged lid 11, and a pouring spout (unnumbered).

The cast iron used in the frying'pan fabrications is described in theliterature as Meehanite type GC-40 and its physical properties arelisted below in Table I. Conventional grey casting have also beenutilized in these fabrications.

' This material meets the requirements outlined in the followingspecifications:

ASTM

ASTM A 126-6 IT ASTM A 1 59-5 8 ASTM A27 8-6 IT ASTM A3 19-53 ASTM A438-60T 00- I -65 2a FEDERAL The stainless steels used in the frying panfabrications were of the chromium-nickel stainless steel series, whosecompositions are listed in Table II. When martensitic stainless steelsof the 400 series (0.08-1 l 0 percent carbon) were employed in trialwelds, equally satisfactory results in respect of weld failure wereobtained.

TABLE II.CHEMICAL REQUIREMENTS OF STAINLES S STEEL Maximum percent Insummary the invention provides a method of fabricating stainlesssteel-cast iron cooking utensils, with economical savings inconstruction materials, taste enhancement of the prepared foods,aesthetic utility and non-failure of the weld seams on prolonged usage.

I claim:

1. In a welded stainless steel cast iron cooking utensil, comprising acast iron cooking surface sheet and a stainless steel jacket housing,having an integrally formed abutment lip projecting inwardly from thejacket housing exterior, and following the direction of the weld seam,the improvement consisting of a tubular, hollow-core, ferritic metalexpansion joint member conforming to the respective circumferences ofthe jacket housing abutment lip and the edge of the cast iron cookingsurface sheet, welded and sandwiched therebetween, thereby forming anintegral unit structure of the jacket housing wall, expansion joint andcast iron cooking surface, said cooking utensil being equipped with anelectric heating source.

2. The improvement as claimed in claim 1, wherein the expansion joint isa ferritic metal having a carbon content of less than 3 per cent.

3. In a welded stainless steel-cast iron frying pan equipped with anelectric heating source and a tiltable trunion stand, said frying pancomprised of a flat cast iron cooking surface sheet and a stainlesssteel jacket housing having an integrally formed abutment lip projectinginwardly from the jacket housing exterior and following the direction ofthe weld scam, the improvement consisting ofa tubular, hollow-core,ferritic metal expansion joint member conforming to the respectivecircumferences of the jacket housing abutment lip and the edge of thecast iron cooking surface sheet, welded and sandwiched therebetween,thereby forming an integral unit structure of the jacket housing wall,expansion joint and cast iron cooking surface.

4. The improvement as claimed in claim 3, wherein the expansion joint isshaped wrought iron tubing.

5. The improvement as claimed in claim 3, wherein the expansion joint isshaped wrought iron sheet.

6. The improvement as claimed in claim 3, wherein the expansion joint isshaped steel tubing.

7. The improvement as claimed in claims 3, wherein the stainless steeljacket housing and the flat cast iron cooking surface sheet are oforbicular shape.

8. The improvement as claimed in claims 3, wherein the stainless steeljacket housing and the flat cast iron cooking surface sheet aresubstantially rectangular in shape.

1. In a welded stainless steel - cast iron cooking utensil, comprising acast iron cooking surface sheet and a stainless steel jacket housing,having an integrally formed abutment lip projecting inwardly from thejacket housing exterior, and following the direction of the weld seam,the improvement consisting of a tubular, hollow-core, ferritic metalexpansion joint member conforming to the respective circumferences ofthe jacket housing abutment lip and the edge of the cast iron cookingsurface sheet, welded and sandwiched therebetween, thereby forming anintegral unit structure of the jacket housing wall, expansion joint andcast iron cooking surface, said cooking utensil being equipped with anelectric heating source.
 2. The improvement as claimed in claim 1,wherein the exPansion joint is a ferritic metal having a carbon contentof less than 3 per cent.
 3. In a welded stainless steel-cast iron fryingpan equipped with an electric heating source and a tiltable trunionstand, said frying pan comprised of a flat cast iron cooking surfacesheet and a stainless steel jacket housing having an integrally formedabutment lip projecting inwardly from the jacket housing exterior andfollowing the direction of the weld seam, the improvement consisting ofa tubular, hollow-core, ferritic metal expansion joint member conformingto the respective circumferences of the jacket housing abutment lip andthe edge of the cast iron cooking surface sheet, welded and sandwichedtherebetween, thereby forming an integral unit structure of the jackethousing wall, expansion joint and cast iron cooking surface.
 4. Theimprovement as claimed in claim 3, wherein the expansion joint is shapedwrought iron tubing.
 5. The improvement as claimed in claim 3, whereinthe expansion joint is shaped wrought iron sheet.
 6. The improvement asclaimed in claim 3, wherein the expansion joint is shaped steel tubing.7. The improvement as claimed in claims 3, wherein the stainless steeljacket housing and the flat cast iron cooking surface sheet are oforbicular shape.
 8. The improvement as claimed in claims 3, wherein thestainless steel jacket housing and the flat cast iron cooking surfacesheet are substantially rectangular in shape.